| Title | Spatio-temporal challenges in dating orogen-scale shear zones: the case of the Himalayan Main Central Thrust |
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| Author | Braden, Z; Godin, L; Kellett, D A ; Yakymchuk, C |
| Source | Tectonophysics vol. 774, 228246, 2019 p. 1-23, https://doi.org/10.1016/j.tecto.2019.228246 |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20190268 |
| Publisher | Elsevier |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf; html; xlsx (Microsoft® Excel®) |
| Area | Himalayas; Simikot; Chuwa River; Humla Karnali River; Tamcha; Dailekh; Chaudhabis River; Nepal |
| Lat/Long WENS | 81.0000 84.0000 30.5000 28.0000 |
| Subjects | geochronology; tectonics; igneous and metamorphic petrology; mineralogy; geochemistry; Science and Technology; Nature and Environment; shear zones; tectonic evolution; orogenies; metamorphism;
deformation; shearing; faulting; displacement; pressure-temperature conditions; crystallography; radiometric dating; argon argon dating; mica; zircon dates; bedrock geology; structural features; faults, thrust; faults, normal; faults, strike-slip;
folds; anticlines; klippen; lithology; sedimentary rocks; igneous rocks; intrusive rocks; granites; foliation; lineations; thermobarometry; spectroscopic analyses; modelling; Himalayan Main Central Thrust; Greater Himalayan Sequence; Lesser Himalayan
Sequence; Main Himalayan Thrust; Main Frontal Thrust; Main Boundary Thrust; Gurla-Mandhata Humla Fault; South Tibetan Detachment; India Craton; Tethyan Sedimentary Sequence; Karnali Klippe; Phanerozoic; Cenozoic; Tertiary |
| Illustrations | location maps; geoscientific sketch maps; cross-sections; columnar sections; photomicrographs; stereonets; graphs; diagrams; phase diagrams; tables; bar graphs; schematic cross-sections |
| Program | Science laboratory network |
| Released | 2019 11 09 |
| Abstract | The spatial extent and dynamic evolution of orogen-scale shear zones renders the determination of the timing and duration of ductile deformation and displacement challenging. The Himalayan Main Central
thrust (MCT) is one of the most widely studied thrust-sense shear zones in the world, particularly regarding its timing, and yet 'when was the MCT active' remains an outstanding question. New and existing pressure-temperature-deformation-time (P-T
-d-t) data from three well-exposed structural sections of the MCT in western Nepal, which together represent>100 km in the direction of tectonic transport, are compared to examine how spatio-temporal variations in recorded shear complicate the answer
to this question. Metamorphic P-T data, quartz microstructures and quartz crystallographic preferred orientation suggest that all three MCT transects underwent similar shear conditions and kinematic behaviour. However, each shear-zone transect
reached peak T conditions during different windows of time. Furthermore, 40Ar/39Ar thermochronology on white mica reveals contrasting timing for the end of ductile deformation. When combined with published monazite and zircon dates, our data indicate
that the record of ductile deformation on the MCT is diachronous in the transport direction and a single shear zone transect is thus not representative of the timing and duration of deformation on the MCT even for a narrow along-strike position. This
study represents the first attempt to track ductile deformation in the direction of thrust propagation at this spatial extent on an orogen-scale thrust system. These results clearly point to the need to study the temporal evolution of shear zones
over significant distances in the direction of tectonic transport, acknowledge potential gaps in the petrochronological record, and incorporate P-T -d data when using shear zone timing and duration results to make regional conclusions. |
| Summary | (Plain Language Summary, not published)
Determining the absolute timing of ancient shear zones remains a scientific challenge because the samples we collect and the minerals within those
samples that we can date using radiometric dating methods preserve an incomplete record of the event we are trying to date. However, small, spatially restricted sample sets are routinely used to date shear zones. In this study, we examine a spatially
extensive geochronological dataset from a well-studied shear zone in the Himalayan orogen, the Main Central thrust. We show the different partial histories of shear recorded in different parts of the shear zone to demonstrate the need for more
spatially extensive studies, and the need for more discussion about potential data gaps in existing studies. |
| GEOSCAN ID | 314896 |
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